This invention concerns the operation of Voltage references dependent on the xe2x80x9cZenerxe2x80x9d or xe2x80x9cAvalanchexe2x80x9d characteristics of a semiconductor diode commonly referred to by those versed in the art as xe2x80x9cZenersxe2x80x9d, Zener Diodes or Zener References. This type of semiconductor device produces a relatively precise voltage across its cathode and anode for a range of currents passing through it in the reverse mode, that is the opposite direction, Cathode to Anode to that which produces normal diode function behaviour. For certain types of these diodes extremely stable voltage behaviour is realisable where the reverse current is set to a suitable and stable value.
It is one of the prime objectives of those making stable voltage reference standards based on the principle to minimise the Very Low Frequency (VLF) noise and long term random instability of output Voltage. It is a further objective to minimise the output voltage dependence on external. environmental conditions particularly variations in temperature and atmospheric pressure.
It is generally known that random noise and instability generated by the Zener diode is reduced by increasing the junction area of the diode. However, this can further be improved by operating the Zener at an optimum current density which reduces the noise but, in a large area diode, can dissipate sufficient power to cause the Zener and its packaging to rise to such high temperature that oven temperature control becomes difficult or impossible without compromising the long term voltage stability of the Zener.
It is accordingly an object of the invention to provide means to operate a Zener diode reference of large junction area at an optimal current density whilst maintaining or controlling the temperature of the silicon chip on which the diode is diffused at a lower increment above the ambient temperature than would have prevailed without application of the invention.
The invention is illustrated by way of example in the accompanying drawings.